"Knowing what trees we have out there and what condition they are in will greatly help us manage the urban forest and develop policies that protect and enhance the urban canopy," says Danielle Bohannan, a botanic specialist with the City of Portland's Urban Forestry division, which organizes the inventory.

The city needs volunteers now for three jobs: collecting tree data outside, leading teams of data collectors and entering the information into a database for analysis. No experience is needed, although team leaders need to attend one training on either June 14 or June 18. (Crew members can sign up and get training anytime.)

Volunteers are trained in how to identify and catalog each tree along a designated route. They measure each tree trunk's diameter, note its species, plot its location and take notes about its overall health.

All of this data gets entered, again by volunteers, into a spatial database that paints a picture of Portland's urban canopy — its species diversity, health and future needs.

Over the past four years, the program has cataloged 70,000 trees in 17 Portland neighborhoods. One major trend: Maples dominate Portland's urban canopy (28 percent), which makes for great fall color, but also more risk of a single pest or disease wiping out many trees.

Having a broader variety of trees is high on the City's priority list.

About half of those were planted by volunteers during community plantings organized with Friends of Trees, says Whitney Dorer, the organization's Neighborhood Trees Manager.

Once the Urban Forestry volunteers collect the tree data, the city uses software to calculate a dollar value for the city's trees. Portland's street trees provide annual benefits ranging from $100,000 to $650,000 per neighborhood, including energy savings, storm water processing, and property value increases, Bohannan says.

Depending on location, replacing all of the trees in a given neighborhood would cost somewhere between $4 million and $20 million.

The inventory findings are presented to neighborhoods at an annual tree summit each fall. From there, residents can use the data to help craft their neighborhood tree plan, which might include addressing older or declining trees, planting new trees or organizing tree walks and pruning workshops.

The neighborhoods participating in the inventory this year are Boise-Eliot, Cully, Foster-Powell, Kerns, Laurelhurst, South Tabor, Sullivan's Gulch and West Portland Park.

If you'd like to see the inventory happen in your neighborhood in 2015, Bohannan advises talking to your neighbors to get a handful of people involved, and then visit portlandoregon.gov/parks/treeinventory to sign up your neighborhood.